In a cellular-based mobile communication system, a large number of base stations are deployed in a wide area, and each base station covers one to about ten small zones known as cells. Here, standardization groups such as 3GPP (3rd Generation Partnership Program) go ahead with the standardization of a system called Self Organizing Network (SON), which autonomously changes parameters of base stations and the like based on the values of radio quality measured by base stations and terminals in a mobile communication system.
For example, NPL 1 describes a SON-related standardization. In the standardization described in NPL 1, the followings are cited as SON use cases: Coverage and Capacity Optimization, Energy Savings, Interference Reduction, Automated Configuration of Physical Cell Identity, Mobility Robustness Optimization, Mobility Load Balancing, RACH Optimization, Automatic Neighbor Relation Function, and the like.
Moreover, NPL 2 describes that methods for the deployment of functions for implementing SON in a wireless system complying with the LTE (Long Term Evolution) standardization are classified as follows.
(1) NM-Centralized SON: the SON algorithm is executed at network management level.
(2) EM-Centralized SON: the SON algorithm is executed at element management level.
(3) Distributed SON: the SON algorithm is executed at network element level.
Moreover, the deployment of the functions in which the SON algorithm is divided and executed at two or more of (1), (2) and (3) above, is known as Hybrid SON.
In the deployment of the functions according to (1) above, the SON algorithm is executed in a centralized manner by a network management system (NMS), which integrates multiple element management systems (EMSs) and secondarily manages base stations.
In the deployment of the functions according to (2) above, the SON algorithm is executed in a centralized manner by an EMS that primarily manages base stations.
In the deployment of the functions according to (3) above, information required for SON is directly exchanged between network elements (here, assumed to be base stations). The SON algorithm is executed by base stations in a distributed manner.
Incidentally, an EMS is provided for each vender of base stations in general. Accordingly, there are some cases where operation information on base stations cannot be transmitted and received between EMSs. In this case, inter-base station interfaces need to be used in order for an EMS in a system with the deployment of the functions according to (2) above to acquire operation information on a neighbor base station out of its own management.
Similarly, there are some cases where operation information on base stations cannot be transmitted and received between NMSs. In this case, inter-base station (or inter-EMS) interfaces need to be used in order for an NMS in a system with the deployment of the functions according to (1) above to acquire operation information on a base station out of its own management.
Note that an inter-base station interface in LTE is defined as the X2 interface in NPL 3. Examples of operation information on a base station transmitted and received over the X2 interface include load information on each cell (RESOURCE STATUS UPDATE) and configuration information on a neighbor cell list and random access channels (ENB CONFIGURATION UPDATE).